The hopcalite catalyst is an oxidation catalyst composed of manganese oxide, copper oxide, and other metallic oxides (such as potassium oxide, silver oxide, or cobalt oxide), and it is known to oxidize and remove carbon monoxide, to clarify sulfur dioxide gas, hydrogen chloride, hydrogen sulfide, or nitrogen oxides, and to remove formaldehyde.
Concrete techniques for treating a gas with the hopcalite catalyst are known. For example, a method wherein the hopcalite catalyst is used as an adsorbent for carbon monoxide to produce an air having properties for a medical application [Japanese Unexamined Patent Publication (Kokai) No. 8-266629], a method wherein the hopcalite catalyst is used as an adsorbent for carbon monoxide, an impurity in an inert gas [Japanese Unexamined Patent Publication (Kokai) No. 10-137530], or a method wherein the hopcalite catalyst is used as a catalyst for removing odor components in a fuel gas [Japanese Unexamined Patent Publication (Kokai) No. 8-24576] are known.
Further, deodorizing techniques with a low temperature plasma are known. For example, an apparatus for a deodorization with the low temperature plasma, composed of a high voltage discharge unit capable of generating a low temperature plasma and a catalyst unit in which a pro-oxidant catalyst is loaded is known (Takuma Giho, Vol.5, No.1, 66-71, 1997). Further, a method for removing an organic solvent, utilizing a low temperature plasma, and a method for removing nitrogen oxides, utilizing a low temperature plasma, as an oxidative effect of a gas are known. In particular, however, a method for converting carbon monoxide in a gas to carbon dioxide, utilizing a low temperature plasma is not known. Further, a technique using the hopcalite catalyst and the low temperature plasma at the same time is not known. Therefore, an enhancement of an activity of the hopcalite catalyst by a low temperature plasma is not known.